1. Field of the Invention
The present invention generally relates to a microscope objective lens and, more particularly, to a Triplet type of low-powered microscope objective lens having a long working distance.
2. Related Background Art
A typical low-powered microscope objective lens of the prior art may be a commercially available 4-powered phase-difference-oriented Plan Achromat offered by the present applicant. This microscope objective lens has a so-called 4-group/4-lens-element construction in which the objective lens is constructed of four lens groups each consisting of a single lens element.
The conventional low-powered Plan objective lens presents, however, such a drawback that a curvature of field is easy to occur when increasing a working distance (a distance along an optical axis between an observed object and a closest-to-object lens surface). In other words, the drawback is that the working distance can not be secured long for keeping well a flatness of the image surface.